A manufacturing method of three-dimensionally shaped object is conventionally known that light beams are irradiated on a powder layer formed of an inorganic or an organic pulverized material so as to form a sintered layer by melting the powder layer, and repeating processes of forming a new powder layer on the sintered layer and irradiation of light beams. In such a manufacturing method, a CO2 laser is mainly used as a light source of the light beams.
Since the CO2 laser is a gas laser, alignment of a resonance mirror of a light beam oscillator inside delicately changes due to fever with laser oscillation, and thus, characteristics such as divergence angle of the light beams, stability of optical axis of the light beams, and stability of the laser output power may vary. Due to variation of characteristics of the light beams, irradiation points of the laser beams, diameters of the focused laser beams and the laser power may be varied. Alternatively, when YAG laser is used as a light source of the light beams, due to thermal balancing of resonance mirrors at both ends of a YAG rod or thermal expansion of the YAG rod itself, characteristics such as divergence angle of the light beams, stability of optical axis of the light beams, and stability of the laser output power may vary just after starting irradiation of light beams, similar to the CO2 laser, and thus, irradiation points of the light beams, diameters of the focused light beams and the laser power may be varied. Therefore, it is necessary to correct the irradiation points of the light beam and so on. The correction of the irradiation points is carried out by irradiating light beams to a photosensitive paper and measuring positions of traces of irradiation of light beams at which the photosensitive paper is discolored by heat of the light beams.
In such a correction method, the output power of the laser in correction, however, is several watts to several tens watts, and is much smaller than the output power of several hundreds watts when sintering powders, actually. Therefore, since oscillation condition of laser at the time of correction is different from that at the time of sintering powders, thermal condition of light beam oscillator varies, and thus, the irradiation points of the light beams do not coincide with the irradiation positions at the time of sintering powders. Thus, correction of the irradiation points of the light beams cannot be corrected sufficiently.
Another manufacturing method of three-dimensionally shaped object is further known that irradiation points of the laser beams are corrected by forming traces with using substantially the same power as that at the time of sintering powders (see patent document 1, for example).
In the manufacturing method shown in the patent document 1, contrast of the traces of the light beams, however, is obscure, so that irradiation points cannot be corrected sufficiently.
[Patent Documents 1]
    Japanese Laid-Open Patent Publication No. 2005-133120